The invention generally relates to a gas lift valve.
For purposes of communicating well fluid to a surface of a well, the well may include a production tubing. More specifically, the production tubing typically extends downhole into a wellbore of the well for purposes of communicating well fluid from one or more subterranean formations through a central passageway of the production tubing to the surface of the well. Due to its weight, the column of well fluid that is present in the production tubing may suppress the rate at which the well fluid is produced from the formation. More specifically, the column of well fluid inside the production tubing exerts a hydrostatic pressure that increases with well depth. Thus, near a particular producing formation, the hydrostatic pressure may be significant enough to substantially slow down the rate at which the well fluid is produced from the formation.
For purposes of reducing the hydrostatic pressure and thus, enhancing the rate at which fluid is produced, an artificial-lift technique may be employed. One such technique involves injecting gas into the production tubing to displace some of the well fluid in the tubing with lighter gas. The displacement of the well fluid with the lighter gas reduces the hydrostatic pressure inside the production tubing and allows reservoir fluids to enter the wellbore at a higher flow rate. The gas to be injected into the production tubing typically is conveyed downhole via the annulus (the annular space surrounding the production tubing) and enters the production tubing through one or more gas lift valves.
As an example, FIG. 1 depicts a gas lift system 10 that includes a production tubing 14 that extends into a wellbore. For purposes of gas injection, the system 10 includes a gas compressor 12 that is located at the surface of the well for purposes of introducing pressurized gas into an annulus 15 of the well. To control the communication of gas between the annulus 15 and a central passageway 17 of the production tubing 14, the system 10 may include several gas lift mandrels 16 (gas lift mandrels 16a, 16b and 16c, depicted as examples). Each one of these gas lift mandrels 16 includes an associated gas lift valve 18 (gas lift valves 18a, 18b and 18c, depicted as examples) that responds to the annulus pressure. More specifically, when the annulus pressure at the gas lift valve 18 exceeds a predefined threshold, the gas lift valve 18 opens to allow communication between the annulus 15 and the central passageway 17. For an annulus pressure below this threshold, the gas lift valve 16 closes and thus, prevents communication between the annulus 15 and the central passageway 17.
It is typically desirable to maximize the number of cycles in which each gas lift valve 18 may be opened and closed, as the cost of the gas lift valves 18 may be a significant component of the overall production costs. The number of times that a gas lift valve may be opened and closed may be a function of the loading that is experienced by the various seals of the gas lift valve 18.